The present invention relates to a pneumatic tire, more particularly to a block pattern tire for use in rough terrain having an improved block arrangement.
Motorcycle tires for use in rough terrain such as motocross tires are generally provided with block-type tread pattern whose negative ratio is over 50% for traction in soft terrain such as mud traction. In such motorcycle tires, the tread camber is very high in comparison with other kinds of tires such as passenger car tire, truck/bus tire and the like, and mud is liable to accumulate in the tread shoulder region during straight running. Therefore, when the running condition changes from straight running to cornering, due to the accumulate mud, road grip and traction are decreased, and control of the machine is liable to be lost.
It is therefore, an object of the present invention to provide a pneumatic tire for use in rough terrain, in which, by improving the arrangement of tread blocks, mud accumulation, traction and the like can be improved, and a running performance change when the running condition changes from straight running to cornering or vice versa is decreased.
According to the present invention, a pneumatic tire comprises a tread comprising central blocks, shoulder blocks and intermediate blocks,
in the tread which is developed in a plane, the central blocks are arranged circumferentially of the tire at substantially constant pitch lengths P1, the intermediate blocks in each of the intermediate regions are arranged circumferentially of the tire at substantially constant pitch lengths P2, and the shoulder blocks in each of the shoulder regions are arranged circumferentially of the tire at substantially constant pitch lengths P3,
in a certain number (K) of circumferential positions, the central blocks are aligned with the intermediate blocks in the tire axial direction, wherein the number (K) is in a range of from 6 to 32,
the circumferential positions are provided circumferentially of the tire at regular intervals equal to the pitch length P1 multiplied by an integral number (n), wherein the number (n) is in a range of from 3 to 8,
the pitch length P2 and pitch length P3 are equal to the pitch length P1 multiplied by n/(nxe2x88x921) or n/(nxe2x88x922),
wherein the central blocks are each defined such that at least 80% of the top face of the block is within a central region centered on tire equator and has a width of 25% of the tread width; the shoulder blocks are each defined such that at least 80% of the top face of the block is within a shoulder region extending from each of tread edges to have a width of 12.5% of the tread width; the intermediate blocks are each defined such that at least 80% of the top face of the block is within an intermediate region between the central region and each of the shoulder regions.